The beginning of the device name specifies the type of block device. Most modern hard disks/[[SSD]] are recognised as SCSI ('''s''') storage '''d'''evices. The type is followed by a lower-case letter listed as {{ic|sd'''x'''}}, where {{ic|'''x'''}} starts from {{ic|a}} for the first device ({{ic|sda}}), {{ic|b}} for the second device ({{ic|sdb}}), and so on. ''Existing'' partitions on those devices will be listed as {{ic|sdx'''Y'''}}, where {{ic|'''Y'''}} is a number starting from {{ic|1}} for the first partition, {{ic|2}} for the second, and so on. In the example above, only one device is available ({{ic|sda}}), and that device has only one partition ({{ic|sda1}}).

+

The beginning of the device name specifies the type of block device. Most modern hard disks/[[SSD]] are recognised as SCSI ('''s''') storage '''d'''evices. The type is followed by a lower-case letter listed as {{ic|sd'''x'''}}, where {{ic|'''x'''}} starts from {{ic|a}} for the first device ({{ic|sda}}), {{ic|b}} for the second device ({{ic|sdb}}), and so on.

+

+

''Existing'' partitions on those devices will be listed as {{ic|sdx'''Y'''}}, where {{ic|'''Y'''}} is a number starting from {{ic|1}} for the first partition, {{ic|2}} for the second, and so on. In the example above, only one device is available ({{ic|sda}}), and that device has only one partition ({{ic|sda1}}).

Note that on [[installation]] of Arch Linux, the output includes those used to host and boot the Arch live media, such as a USB drive. Not all devices listed are therefore viable or appropriate mediums for installation; results ending in {{ic|rom}}, {{ic|loop}} or {{ic|airoot}} can be ignored.

Note that on [[installation]] of Arch Linux, the output includes those used to host and boot the Arch live media, such as a USB drive. Not all devices listed are therefore viable or appropriate mediums for installation; results ending in {{ic|rom}}, {{ic|loop}} or {{ic|airoot}} can be ignored.

Revision as of 21:23, 29 August 2016

This article deals with so-called core utilities on a GNU/Linux system, such as less, ls, and grep. The scope of this article includes, but is not limited to, those utilities included with the GNU coreutils package. What follows are various tips and tricks and other helpful information related to these utilities.

Basic commands

The following table lists basic shell commands every Linux user should be familiar with. Commands in bold are part of the shell, others are separate programs called from the shell. See the below sections and Related articles for details.

Command

Description

Example

man

Show manual page for a command

man ed

cd

Change directory

cd /etc/pacman.d

mkdir

Create a directory

mkdir ~/newfolder

rmdir

Remove empty directory

rmdir ~/emptyfolder

rm

Remove a file

rm ~/file.txt

rm -r

Remove directory and contents

rm -r ~/.cache

ls

List files

ls *.mkv

ls -a

List hidden files

ls -a /home/archie

ls -al

List hidden files and file properties

mv

Move a file

mv ~/compressed.zip ~/archive/compressed2.zip

cp

Copy a file

cp ~/.bashrc ~/.bashrc.bak

chmod +x

Make a file executable

chmod +x ~/.local/bin/myscript.sh

cat

Show file contents

cat /etc/hostname

strings

Show printable characters in binary files

strings /usr/bin/free

find

Search for a file

find ~ -name myfile

mount

Mount a partition

mount /dev/sdc1 /media/usb

df -h

Show remaining space on all partitions

ps -A

Show all running processes

killall

Kill all running instances of a process

ss -at

Display a list of open TCP sockets

cat

Because cat is not a built-in shell, on many occasions you may find it more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact < file does the same as cat file.

cat is able to work with multiple lines, although this is sometimes regarded as bad practice:

$ cat << EOF >> path/filefirst line
...
last line
EOF

A better alternative is the echo command:

$ echo "\
first line
...
last line" \
>> path/file

If you need to list file lines in reverse order, there is a utility called tac (cat reversed).

dd

dd is a command on Unix and Unix-like operating systems whose primary purpose is to convert and copy a file.

By default, dd outputs nothing until the task has finished. To monitor the progress of the operation, add the status=progress option to the command. See the manual for more information.

Note:cp does the same as dd without any operands but is not designed for more versatile disk wiping procedures.

grep

grep (from ed's g/re/p, global/regular expression/print) is a command line text search utility originally written for Unix. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.

Remember that grep handles files, so a construct like cat file | grep pattern is replaceable with grep patternfile

find

find is part of the findutils package, which belongs to the base package group.

One would probably expect a find command to take as argument a file name and search the filesystem for files matching that name. For a program that does exactly that see #locate below.

Instead, find takes a set of directories and matches each file under them against a set of expressions. This design allows for some very powerful "one-liners" that would not be possible using the "intuitive" design described above. See UsingFind for usage details.

locate

Install the mlocate package. After installation a script is automatically scheduled to run a daily task to update its database. You can also manually run updatedb as root at any time. By default, paths such as /media and /mnt are ignored, so locate may not discover files on external devices. See updatedb(1) for details.

The locate command is a common Unix tool for quickly finding files by name. It offers speed improvements over the find tool by searching a pre-constructed database file, rather than the filesystem directly. The downside of this approach is that changes made since the construction of the database file cannot be detected by locate. This problem is minimised by regular, typically scheduled use of the updatedb command, which (as the name suggests) updates the database.

Before locate can be used, the database will need to be created. To do this, execute updatedb as root.

The beginning of the device name specifies the type of block device. Most modern hard disks/SSD are recognised as SCSI (s) storage devices. The type is followed by a lower-case letter listed as sdx, where x starts from a for the first device (sda), b for the second device (sdb), and so on.

Existing partitions on those devices will be listed as sdxY, where Y is a number starting from 1 for the first partition, 2 for the second, and so on. In the example above, only one device is available (sda), and that device has only one partition (sda1).

Note that on installation of Arch Linux, the output includes those used to host and boot the Arch live media, such as a USB drive. Not all devices listed are therefore viable or appropriate mediums for installation; results ending in rom, loop or airoot can be ignored.

iconv

iconv converts the encoding of characters from one codeset to another.

The following command will convert the file foo from ISO-8859-15 to UTF-8 saving it to foo.utf:

$ iconv -f ISO-8859-15 -t UTF-8 foo >foo.utf

See man iconv for more details.

Convert a file in place

Tip: You can use recode instead of iconv if you do not want to touch the mtime.

Unlike sed, iconv does not provide an option to convert a file in place. However, sponge can be used to handle it, it comes with moreutils.

$ iconv -f WINDOWS-1251 -t UTF-8 foobar.txt | sponge foobar.txt

See man sponge for details.

ip

ip allows you to show information about network devices, IP addresses, routing tables, and other objects in the Linux IP software stack. By appending various commands, you can also manipulate or configure most of these objects.

Note: The ip utility is provided by the iproute2 package, which is included in the base group.

Object

Purpose

Manual Page Name

ip addr

protocol address management

ip-address

ip addrlabel

protocol address label management

ip-addrlabel

ip l2tp

tunnel Ethernet over IP (L2TPv3)

ip-l2tp

ip link

network device configuration

ip-link

ip maddr

multicast addresses management

ip-maddress

ip monitor

watch for netlink messages

ip-monitor

ip mroute

multicast routing cache management

ip-mroute

ip mrule

rule in multicast routing policy db

ip neigh

neighbour/ARP tables management

ip-neighbour

ip netns

process network namespace management

ip-netns

ip ntable

neighbour table configuration

ip-ntable

ip route

routing table management

ip-route

ip rule

routing policy database management

ip-rule

ip tcp_metrics

management for TCP Metrics

ip-tcp_metrics

ip tunnel

tunnel configuration

ip-tunnel

ip tuntap

manage TUN/TAP devices

ip xfrm

manage IPsec policies

ip-xfrm

The help command is available for all objects. For example, typing ip addr help will show you the command syntax available for the address object. For advanced usage see the iproute2 documentation.

Note: You might be familiar with the ifconfig command, which was used in older versions of Linux for interface configuration. It is now deprecated in Arch Linux; you should use ip instead.

less

This article or section needs expansion.

Reason: less is a complex beast, and this section should explain some of the basic less commands (Discuss in Talk:Core utilities#)

less is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pagers such as more and pg, less offers a more advanced interface and complete feature-set.

number of hard links for the entity; files will have at least 1, i.e. the showed reference itself; folders will have at least 2: the showed reference, the self-referencing . entry, and then a .. entry in each of its subfolders;

File names containing spaces enclosed in quotes

By default, file and directory names that contain spaces are displayed surrounded by single quotes. To change this behavior use the -N or --quoting-style=literal options. Alternatively, set the QUOTING_STYLEenvironment variable to literal. [2]

mv

This alias suspends mv after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

od

The od (octal dump) command is useful for visualizing data that is not in a human-readable format, like the executable code of a program, or the contents of an unformatted device. See the manual for more information.

pv

This article or section needs language, wiki syntax or style improvements. See Help:Style for reference.

rm

This alias suspends rm after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute -I with -i if you prefer to confirm even for one file.

Zsh users may want to put noglob before timeout to avoid implicit expansions.

To remove directories known to be empty, use rmdir as it fails in case of files inside the target.

tar

As an early Unix archiving format, .tar files—known as "tarballs"—are widely used for packaging in Unix-like operating systems. Both pacman and AUR packages are compressed tarballs, and Arch uses GNU'star program by default.

For .tar archives, tar by default will extract the file according to its extension:

$ tar xvf file.EXTENSION

Forcing a given format:

File Type

Extraction Command

file.tar

tar xvf file.tar

file.tgz

tar xvzf file.tgz

file.tar.gz

tar xvzf file.tar.gz

file.tar.bz

bzip -cd file.bz | tar xvf -

file.tar.bz2

tar xvjf file.tar.bz2bzip2 -cd file.bz2 | tar xvf -

file.tar.xz

tar xvJf file.tar.xzxz -cd file.xz | tar xvf -

The construction of some of these tar arguments may be considered legacy, but they are still useful when performing specific operations. See its man page with man tar for details.

which

which shows the full path of shell commands. In the following example the full path of ssh is used as an argument for journalctl:

# journalctl $(which sshd)

wipefs

wipefs can list or erase file system, RAID or partition-table signatures (magic strings) from the specified device. It does not erase the file systems themselves nor any other data from the device.

See wipefs(8) for more information.

For example, to erase all signatures from the device /dev/sdb and create a signature backup ~/wipefs-sdb-offset.bak file for each signature: